Rotor position information is in general required for the stable operation of permanent magnet AC motors having sinusoidal current excitation. Continuous rotor position has been obtained in the past from encoders mounted on the motor shaft or indirectly through estimation algorithms based on voltage and current feedback. The latter is preferred because it results in lower system and operating cost.
However, most passive rotor estimation schemes (based on measured voltage and current) are complex and require precise knowledge of the motor parameters such as resistance and inductance. However, these parameters, particularly the stator resistance, change widely with temperature. This leads to inaccuracy in rotor angle estimation and results in control stability problems, reduced torque per ampere capability and degradation of motor operating efficiency.
It would therefore be desirable to produce a rotor angle estimation scheme which provides maximum torque per ampere performance without requiring accurate knowledge of the stator resistance or other motor parameters.